Heat a heavy pan over medium-high heat. Add the ground beef and chopped onion; cook until the beef browns and the onion becomes tender, about 6–8 minutes.

Drain excess fat. Stir in the refried beans and taco seasoning; the mixture should thicken.

Squeeze the lime over the beef mixture and stir in the chopped cilantro. Taste and adjust salt or lime if needed. Set aside.

Spray a 13×9-inch baking dish with nonstick spray. In a large bowl, whisk together the condensed soup and sour cream until smooth.

Spoon a thin layer of the sour-cream mixture into the bottom of the dish. Lay half-cut tortillas flat along the edges and three halves across the center to cover the bottom.

Spread half the beef mixture evenly over the tortillas and sprinkle 1 cup of shredded cheese on top.

Repeat with another layer of sour-cream mixture, tortillas, beef, and cheese. Finish with remaining cheese on top.

Preheat the oven to 350°F (175°C). Bake uncovered for 20 minutes if fresh, or 30 minutes if chilled, until edges bubble and cheese turns golden.

Let rest for 5–10 minutes before slicing.